Euro-limpacs Deliverables

ABSTRACT - DELIVERABLE 107

Report on results of experimental manipulations at Gårdjsön catchment

Mercury (Hg) is a naturally occuring element originating from mineral ores where it is present as Cinnober (HgS). Human activities have increased the mobilisation of mineral mercury causing con-tamination of air, water and soils. The main release mechanisms are mining and subsequent use in in-dustry and combustion of fossil fuels, mainly coal. The environmental cycling of Hg is complex and involves transformations and transfers between different compartments (air, water, soils, biota). Atmospheric dispersion is the main global transport pathway of Hg. Elemental Hg vapour (Hg0) is volatile and relatively chemically stable which makes long-range transport feasible (Lindberg et al., 2007).

Anthropogenic activities have increased the levels of Hg in all compartments of the environment via emissions and mobilisation of Hg. In Boreal regions, Hg is efficiently accumulated in forest soils associated with organic material. Indirectly, human activities may also enhance the negative impacts of Hg accumulated in the environment e.g. via increasing the mobility of Hg and increasing the availability of MeHg for uptake in food chains. Examples of such activities include the construction of hydrological reservoirs for electricity generation (Verta, Rudd) where Hg in the inundated soils is mobilised and forest practices (Garcia and Carignan, 1999; 2000; 2005; Porvari et al., 2003; Munthe and Hultberg, 2004). In the case of forestry practices, effects on the leaching of MeHg in particular have been observed over long time periods.

This study was focused on the impacts of increasing precipitation amounts on Hg and MeHg re-leases from forest soils to water. For certain areas of Sweden, increased rainfall is predicted as one of the major climate change effects in addition to temperature increases. Increased precipitation will lead to increased ground water table levels, increased soil saturation and increased run-off. This is a situation which is similar to flooding for hydrological reservoirs although the extent of the hydrological change is significantly smaller. The main objective of this study was to investigate if increased rain fall woul dincrease the leaching of MeHg from forest soils to the aquatic ecosystems.

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